This invention relates in general to precise mechanical mounting structures and methods for securing hard gem-like implements. More specifically, it relates to the secure mounting of a prism-shaped sapphire blade in a V-shaped groove of a holder.
It is known to use a sapphire blade for finish-scraping operations in a magnetic tape cleaning and reconditioning instrument; see for example U.S. Pat. Nos. 3,035,295; 3,587,128; and 3,616,478. Tools employing sapphire blades are also used for other scraping operations, as well as for cutting and like purposes. Sapphire is used in these industrial applications because it is extremely hard and dense, resists wear, holds a sharp edge, and in general has a long operational life in bladed tool. However, the relatively high cost of sapphire makes it desireable to form a sapphire blade in a shape that requires a minimum volume of the gem material per working edge. Further limitations on the configuration of a sapphire blade stem from the extreme hardness and brittleness of the material; the latter property renders sapphire implements prone to chipping and cracking, even during manufacture. In addition, industrial applications require that the blade be accurately positioned, and yet often be in a holder that can be readily removed and replaced.
Heretofore, as exemplified for example by tape cleaning instruments available from Kybe Corporation of Waltham, Massachusetts (the assignee hereof), the foregoing objectives for sapphire bladed tools were met by using a sapphire blade having a prism shape and by mounting the blade in a mating groove recessing the supporting holder. The edges of the blade are the two longitudinal edges of the prism which extend above the mounting groove. This arrangement provides two blade edges as desired, and the holder supports the blade to provide the requisite strength. Further, the prism shape requires only a relatively small amount of sapphire. For example, the quantity of sapphire required for a prism-shaped blade compares favorably with the quantity used in the more complexly configured sapphire blade disclosed in U.S. Pat. No. 3,616,478 of Martz et al (a bar-shaped blade with inflected sides).
Although a prism configuration offers these advantages, it has a significant shortcoming in that it is difficult to mount the blade securely in a holder with a high degree of reliability and at low production cost. The smooth converging surfaces of the prism configuration provide little, if any, anchorage for securing the blade to the holder. The prior practice has been to adhesively bond these abutting surfaces, Sapphire, however, is so dense, smooth and hard that it does not readily form adhesive bonds.
In an effort to establish a secure bond, the prior art has used adhesives set under considerable pressure of the prism blade into the mounting groove. However, the pressure levels used to form the bond often are sufficient to crack the sapphire, which completely destroys the blade. One manifestation of this problem has been that sapphire prism blades have heretofore been restricted to relatively short lengths, in the order of two and one half inches. Moreover, even when a seemingly satisfactory bond is achieved without cracking the sapphire, the bond is sufficiently unreliable to require destructive testing of each batch of blades thus mounted. If a bond fails upon such testing, the entire batch is discarded. Such test losses, as well as failures in use, substantially increase production costs and limit the effectiveness of employing sapphire bladed tools.
It is therefore a principal object of this invention to provide a mounting structure and method for a prism-shaped gem-like blade which is comparatively strong, reliable and inexpensive, and which does not subject the gem material to excessive forces or pressures.
Another object is to provide a mounting structure and method for a prism-shaped sapphire blade that accurately and permanently positions the blade in a holder. It is also an object that the mount positively lock the blade to the holder.
A further object is to provide a mounting structure and method of the above character that allows the mounting of sapphire and like gem blades having greater length than was heretofore considered economical.
Other objects of the invention will in part be obvious and will in part appear hereinafter.